The present invention relates to a rotational apparatus including one or more passive magnetic bearing(s) that exert radially centering forces on a rotatable element as well as axial force on the rotatable element while the rotor rotatable element is rotating. In an embodiment of the invention, the passive magnetic bearing (s) are formed of a tapered magnetic ring in a rotor and a tapered array of shorted conducting circuits in a stator where the stator also includes non-shorted conducting circuits for current generation and/or for exerting torque on the rotor.
One conventional technique to drive a rotatatable element, such as a rotor or an impeller, of a rotational apparatus is through the use of an impeller drive shaft. The impeller drive shaft often penetrates a housing and the driven fluid to connect to a center hub of the impeller. Such a configuration causes the impeller drive shaft to travel through the pump housing and the driven fluid, thus, requiring features such as fluid seals or shaft housings to seal the shaft as it penetrates the housing to prevent the driven fluid from exiting the housing through the point of shaft entry.
Recent improvements in rotational apparatus technology have eliminated the need for the drive shaft to drive an impeller of a rotational apparatus and therefore, have eliminated the need for drive shaft seals and drive shaft housings. One improvement incorporates magnets or electromagnets in an impeller drive assembly in place of a drive shaft. However, a magnetic or an electromagnetic drive assembly alone still requires a mechanical bearing affixed to a spindle or shaft on which the impeller is mounted. One drawback to this arrangement is that the mechanical bearing tends to wear over time requiring maintenance, downtime, and at some point replacement. Further, mechanical bearings still require one or more seals to prevent contamination of the bearing, the driven fluid, or both. Unfortunately, the mechanical seals tend to leak over time requiring maintenance and replacement.
Other recent improvements in rotational apparatus technology include an active magnetic bearing assembly, separate from the magnetic drive assembly, in place of the mechanical bearing. For an active magnetic bearing assembly, placement of the magnetic bearing assembly in relation to the magnetic drive assembly is critical in order to avoid magnetic interference between the active magnetic bearing assembly and the magnetic drive assembly because each magnetic assembly generates a unique and exclusive magnetic field. Avoiding magnetic interference puts extensive constraints on relative locations and geometries of the magnetic drive assembly and the magnetic bearing assembly. Further, a separate active magnetic bearing assembly and a separate magnetic drive assembly often require complex control systems to compensate for changes in magnetic field strength during operation of the rotational apparatus such as at start up, shutdown, acceleration, or deceleration. In the case of sudden loss of power, an active magnetic bearing assembly ceases to operate which can lead to sudden catastrophic failure of the rotational apparatus.
In contrast, in the event of sudden power loss power loss, passive magnetic bearings continue to function until the rotational speed of a rotatable element falls below a critical value, which greatly reduces the risk of sudden and catastrophic failure of the rotational apparatus. Additionally, a passive magnetic bearing assembly may produce less interference with an active magnetic drive assembly. However, passive magnetic bearings may greatly increase the complexity of a rotational apparatus by requiring a rotatable element to have separate magnetic arrays for a drive assembly, a first magnetic bearing assembly for radial centering, and a second magnetic bearing assembly to prevent contact between the rotatable element and a stationary element in an axial direction.
Thus, there exists a need for a rotational apparatus that incorporates one or more passive magnetic bearing(s) that radially center a rotatable element, such as a rotor, and that prevent contact between the rotatable element and a stationary element along an axis of rotation. A magnetic array used for the passive magnetic bearing should also be used to generate power and/or generate torque on the rotatable element.